JP2015079881A - Structure of semiconductor device comprising Cu2O film as p-type semiconductor layer and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a structure of a semiconductor device such as a solar battery device which enables the deposition of a CuO film on substrates of various materials, and the large reduction in a process temperature for film formation, and which is expected to be able to offer the same performance as that at a high temperature; and a method for manufacturing such a structure of a semiconductor device.SOLUTION: A semiconductor device comprises: a CuO film 4 as a p-type semiconductor layer. The CuO film 4 is composed of a polycrystalline film having a thickness of 100-1000 nm, in which orientation directions of crystal planes of crystal grains are selected to be only one direction. At least 80% of the crystal grains forming the polycrystalline film are exposed from both the surfaces of the polycrystalline film. A method for manufacturing a semiconductor device comprises at least the steps of: forming a metal film; depositing a CuO film 4; and performing a thermal treatment for re-crystallization. In the step of forming the metal film, a metal film 3 having a work function of a value comparable to or larger than that of CuO is formed on the substrate 1. In the step of depositing the CuO film, the CuO film 4 forming a p-type semiconductor layer is directly deposited directly on the metal film 3 at a room temperature to a temperature of 400°C. In the step of performing the thermal treatment for re-crystallization, the CuO film 4 is re-crystallized by performing a thermal treatment at 400°C-600°C while controlling an oxygen partial pressure in a range of 0.1-10 Pa.

Description

The present invention can also be applied as a rectifier element, a thin film transistor element using Cu ₂ O as a channel layer, a variable resistance nonvolatile memory element, an ultraviolet sensor element, and the like, and particularly suitable for use as a solar cell element. _{The present} invention relates to a semiconductor device including a ₂ O film as a p-type semiconductor layer and a method for manufacturing the same.

Solar cells using oxide semiconductors have features such as abundant resources, low cost, and low toxicity, and have been studied as candidates for next-generation environmentally friendly low-cost solar cell elements. ing. In a solar cell using an oxide semiconductor, the oxide semiconductor has a relatively high light absorption coefficient, a narrow band gap energy, and a high carrier mobility among oxide semiconductors, and can obtain p-type semiconductor characteristics. Copper (Cu ₂ O) is often used as a light absorber layer, and a heterojunction type solar cell with another n-type oxide semiconductor or a metal can be realized.

Conventionally, many examples have been proposed as a structure and manufacturing method of a solar cell using a Cu ₂ O film (see Patent Document 1), but the highest energy conversion efficiency of 5.38% has been obtained at present. An example relating to the thermal oxidation method is described in Non-Patent Document 1. The Cu ₂ O layer is formed by high-temperature thermal oxidation at 1050 ° C. using a 100 μm thick copper plate. The solar cell structure is a p / n heterojunction diode type using Al-doped ZnO (AZO) as an n-type oxide semiconductor layer, and several materials were compared as a thin buffer layer inserted between p / n. The results are stated.

The p / n heterojunction diode type solar cell using Cu ₂ O as the p-type light absorption layer has the maximum theoretical solar energy conversion efficiency due to the optical band gap of Cu ₂ O, 2.1 eV. If this conversion efficiency is realized, a new solar cell with low cost and high environmental friendliness can be obtained. The energy conversion efficiency strongly depends on the crystal quality of the Cu ₂ O layer, but in general, the higher the formation temperature, the higher the quality crystallinity is obtained. This is an oxide solar cell using a Cu ₂ O layer formed by an oxidation method. The Cu ₂ O layer by this high-temperature thermal oxidation method has a polycrystalline structure, but very large crystal grains are obtained, and electrical characteristics such as carrier mobility are almost the same as single crystal Cu ₂ O. Has been obtained.

JP 2007-13098 A

Yuki Nishi et al .: “Effect of inserting a thin buffer layer on the efficiency in n-ZnO / p-Cu2O heterojunction solar cells”, Journal of Vacuum Science and Technologies, Vol. A 30, 04D103 (2012).

However, when the Cu ₂ O layer is formed by the high temperature thermal oxidation method, since the processing temperature is a high temperature exceeding 1050 ° C., uniform temperature control over a large area is difficult and the thermal load is large, High energy consumption is considered to hinder mass production. Moreover, since it is necessary to use a metal copper plate as a board | substrate, there exists a problem that the application method to semiconductor elements, such as a solar cell element, is limited.

The present invention can greatly reduce the Cu ₂ O film formation process temperature, deposit Cu ₂ O films on substrates of various materials, and at the same time as when the process temperature is increased. It is an object of the present invention to provide a structure of a semiconductor element such as a solar cell element that can be expected to have a high performance and a method for manufacturing the same.
In addition, an additional object is to make it easier to control unknown crystal quality factors that limit electrical properties.

The polycrystalline structure in which the crystal grain interface exists and the plane orientation of each crystal grain is in a random direction has more electrical characteristics than a single crystal with no grain boundary and a single crystal plane. Although significantly inferior, a polycrystalline thin film that can be formed relatively easily for practical industrial use at a lower cost is effective. It is a general interpretation that the electrical characteristics of a polycrystalline thin film are better as the crystal grains are larger and the grain boundaries are smaller, and as the formation temperature is higher, a larger crystal grain size is obtained.
When using a Cu ₂ O film as a light absorption layer for solar cells, it is very difficult to reduce the thickness of a single crystal, and it is practical to use a polycrystalline film. In order to increase the temperature, it is one process guideline to perform at a high forming temperature for the above-described reason, and therefore, mere reduction of the forming temperature leads to deterioration of various electrical characteristics.

Therefore, the following means 1) and 2) are used in order to compensate for the reduction in various characteristics accompanying the reduction in crystal grain size due to the reduction in the formation temperature of the Cu ₂ O film.
1) Uniform crystal plane orientation of each crystal grain in the same direction to prevent characteristic degradation due to quantum effective fluctuations due to random crystal orientation.
2) Prevent the disappearance of charges at the grain boundaries by minimizing or eliminating the number of crystal grain interfaces across the film thickness direction (vertical direction), which is the drift direction of charges generated by absorbed light.
In addition, preferably, further improvement in performance can be expected by using the following means 3).
3) The crystal structure and the type and density of defects in each crystal grain are controlled by appropriate and precise post-processing of the highly oriented polycrystalline film.

Specifically, by using a metal film such as Pt that is self-organized and deposited on the substrate in a (111) plane orientation as the lower electrode, a Cu ₂ O film is deposited on the substrate at a low temperature of 400 ° C. or lower. A Cu ₂ O film having a small crystal grain size oriented to the (111) plane, a smooth surface roughness of about several nanometers and good film thickness uniformity is deposited to a thickness of about 0.1 to 1 μm. Next, rapid thermal annealing (hereinafter sometimes referred to as “RTA”) in a gas atmosphere with high-precision control of the oxygen gas partial pressure at temperatures of about 400 ° C. to 600 ° C. for about 30 seconds to several minutes. A Cu ₂ O polycrystalline film strongly oriented in the (111) plane is produced by performing crystal grain growth by performing a short-time heat treatment. When the thickness of the Cu ₂ O film is approximately 1 μm or less, almost single crystal grains can be formed in the film thickness direction (vertical direction) by adjusting the RTA conditions as described above [that is, the polycrystalline film In any observation region of the cross section, among all the crystal grains in the observation region, the ratio of the crystal grains exposed on both surfaces (upper and lower surfaces) of the polycrystalline film is 80% or more, more preferably 90% or more, most preferably Therefore, it is possible to eliminate the crystal grain interface as much as possible in the film thickness direction. At the same time, each crystal grain continuous across the crystal grain boundary in the in-plane direction (horizontal direction) becomes a single crystal with almost all (111) orientation. The plane orientation of Cu ₂ O crystal grains tends to decrease as the deposited film thickness increases. However, when using a Cu ₂ O film as a light absorption layer of a solar cell, since the light absorption coefficient of visible light is very high, if the film thickness is about 1 μm, the absorption rate of light energy will be sufficient. . Also, the thinner the film, the easier it is to form an ideal film that is close to a single crystal.Thus, if some optical confinement structure is used, sufficient light absorption can be obtained even with a thinner film thickness, and the energy is closer to the single crystal characteristics. A significant improvement in conversion efficiency can be expected.

In addition, when the Cu ₂ O layer has such a structure, a thin Cu ₂ O single crystal grain can be obtained by controlling the oxygen gas partial pressure in the atmospheric gas with high accuracy during crystal grain growth in the RTA process. The oxygen deficiency (V _o ) acting as a donor (electron supply source) and a Cu deficiency acting as an acceptor (hole supply source) can be directly controlled in the oxygen gas supply to the crystal lattice. It becomes possible to control flexibly with high accuracy so that the density of (V _cu ) and the density ratio thereof are preferable values for improving the performance of the solar cell element.
Using the above means, a Cu ₂ O polycrystalline structure layer was produced, and a heterojunction p / n diode type solar cell element using this as a p-type light absorption layer was produced.

The present invention is to solve the above-mentioned problems based on the above-described means, and according to this application, the following invention is provided.
<1> A semiconductor element comprising a Cu ₂ O film as a p-type semiconductor layer, wherein the Cu ₂ O film has a thickness in which the crystal plane orientation direction of each crystal grain is selected only in one direction. A semiconductor element, which is a polycrystalline film having a thickness of 100 to 1000 nm, and 80% or more of crystal grains constituting the polycrystalline film are exposed on both sides of the polycrystalline film.
An oxide solar cell element comprising _<2> Cu 2 O layer as the p- type semiconductor layer of the Cu ₂ O film, the crystal face orientation of each crystal grain is selected only in one direction An oxide solar cell characterized in that it is a polycrystalline film having a thickness of 100 to 1000 nm, and 80% or more of the crystal grains constituting the polycrystalline film are exposed on both sides of the polycrystalline film element.
<3> On a substrate, a metal film having a face-centered cubic lattice atomic arrangement structure having a work function value equal to or higher than that of Cu ₂ O as a lower electrode, the Cu ₂ O film, and ZnO as a buffer layer The oxide solar cell element according to <2>, further including a layer and an AZO layer as an n-type semiconductor layer in this order, and having a heterojunction diode structure.
<4> The oxide solar cell element according to <3>, further including a metal nanodot antenna structure for generating surface plasmon resonance immediately above the ZnO buffer layer.
<5> The oxide solar cell element according to <3> or <4>, wherein the metal film is selected from a Pt film, an Au film, a Ni film, a Pd film, and an Ir film.
<6> A metal film forming step for forming a metal film having a face-centered cubic lattice atomic arrangement structure having a work function value equal to or greater than that of Cu ₂ O on the substrate, and a p- Cu ₂ O film deposition process for depositing Cu ₂ O film to be a semiconductor layer of room temperature at room temperature to 400 ° C., and heat treatment at 400 ° C. to 600 ° C. while adjusting the oxygen partial pressure in the range of 0.1 to 10 Pa the method for manufacturing a semiconductor element or an oxide solar cell device according to any one of <1> to <5> the recrystallization heat treatment process comprising at least performing a recrystallization of Cu ₂ O film by performing.
<7> one of Cu ₂ O deposited film thickness of the Cu ₂ O film deposition step was 200nm with maximum, and a Cu ₂ O layer deposition step and subsequent recrystallization heat treatment process is repeated a plurality of times according to <6> A method for manufacturing a semiconductor element or an oxide solar cell element.

The present invention can include the following aspects.
<8> The semiconductor element according to <1>, wherein a ratio of crystal grains exposed on both surfaces of the polycrystalline film among crystal grains constituting the polycrystalline film is 90% or more.
<9> The oxide solar cell according to any one of <2> to <5>, wherein a ratio of crystal grains exposed on both surfaces of the polycrystalline film is 90% or more among crystal grains constituting the polycrystalline film. element.
<10> The oxide solar cell element according to <4> or <5>, wherein the metal of the metal nanodot antenna structure is one or more alloys selected from Ag, Au, Cu, and Al.
<11> Any of <3> to <5>, wherein the substrate is selected from a silicon substrate whose surface is oxidized, a glass substrate, an amorphous silicon substrate, various engineering plastic substrates, various polymer resin films, and various metal foils 2. The oxide solar cell element according to item 1.
<12> between the metal film forming step and Cu ₂ O film deposition process, a method for manufacturing a semiconductor element or an oxide solar cell device according to <6> or <7> including a metal film heat treatment step.

According to the present invention, in the Cu ₂ O polycrystalline layer serving as the light absorption layer of the oxide semiconductor solar cell, the orientation planes of the respective crystal grains are aligned in a single direction, and only one in the film thickness direction. The light absorption rate is sufficient for crystal grains to be formed and the polycrystalline structure is as thin as possible, so that the quantum effective fluctuation due to the randomness of the polycrystalline structure is reduced. In addition, since there are very few crystal grain interfaces in the film thickness direction, which is the drift direction of charges generated by light absorption, the loss of charge transfer in the film thickness direction is reduced. The performance improvement as a semiconductor device by reducing the quantum effective fluctuation and the loss of charge transfer is as follows: a rectifying device, a thin film transistor device using Cu ₂ O as a channel layer, a variable resistance nonvolatile memory device, an ultraviolet sensor device This can also be expected when used as a semiconductor device comprising a Cu ₂ O film such as p-type semiconductor layer. For this reason, even if it is a polycrystalline structure with a small crystal grain size obtained without using a high-temperature formation process exceeding 1000 ° C, the good basic physical properties inherent to single crystals will be partially developed. In addition, the process temperature can be significantly reduced while suppressing deterioration of various electrical characteristics.

In addition, a (111) -oriented metal film such as a (111) -oriented Pt film that also serves to promote self-organized oriented growth of the Cu ₂ O crystal and the lower electrode is used as the base for forming the Cu ₂ O layer. Therefore, the solar cell element is formed on any material substrate in which the self-organized orientation of the (111) plane of the metal film occurs and the process heat resistance and strength required in the subsequent steps of manufacturing electronic devices such as solar cells. It is possible to form a semiconductor element such as. The (111) plane orientation of a metal film such as a Pt film is formed in a self-organized manner on the surface of many amorphous material substrates such as a silicon substrate or a glass substrate having an oxidized surface.

In addition, the Cu ₂ O layer according to the present invention was first formed on a metal film at a low temperature of 400 ° C. or lower at a low temperature of 400 ° C. or less while forming a smooth thin film having a small crystal grain size and high film thickness uniformity on the (111) plane. By continuously performing RTA treatment at 400 ° C. to 600 ° C., a thin polycrystalline structure film (arbitrary cross section) that is strongly oriented in the (111) plane and composed of almost single crystal grains in the film thickness direction (A polycrystalline structure film in which more than 80% of crystal grains in a randomly selected observation region are exposed on both sides of the film) is formed, so the amount of oxygen supplied to a thin single crystal grain during crystal grain growth It is possible to control the crystal defect density such as V _o and V _cu and their ratio with high accuracy and form a Cu ₂ O layer with more excellent electrical characteristics. It becomes possible. In the heat treatment process for crystal grain growth, more than 80% of materials that are effective in controlling the carrier density of Cu ₂ O were exposed on both sides of the film using various source gases and raw materials. There is a possibility that Cu ₂ O having characteristics more preferable as a semiconductor element such as a solar cell element can be formed by effectively vapor phase diffusion or solid phase diffusion to crystal grains.

Furthermore, in the method of forming a Cu ₂ O layer according to the present invention, the film formation and deposition temperature is room temperature to about 400 ° C., and the film is heat-treated by RTA at 400 ° C. to 600 ° C. for a very short time. Therefore, the thermal load on the device is greatly reduced, the flexibility of process design is increased, and the range of device application is expanded. Furthermore, it is expected that the energy consumption during production accompanying the heat treatment will be greatly reduced.

The X-ray diffraction pattern which shows the copper oxide film quality change for demonstrating the principle of this invention. (a) is a case where copper oxide is formed on the SiO ₂ substrate of the comparative example, (b) is a case where copper oxide is formed on the Pt film of the embodiment of the present invention, and (c) is a more detailed view of (a). (D) shows a more detailed analysis result of (b). Cu ₂ O layer cross-sectional TEM photograph and tracing diagram for explaining the principle of the present invention. (a) shows the case where copper oxide is formed on the SiO ₂ substrate of the comparative example, and (b) shows the case where copper oxide is formed on the Pt film of the example of the present invention. Photoluminescence data for explaining the principle and effectiveness of the present invention. The case where copper oxide is formed on the Pt film of the example of the present invention is shown in comparison with the case where copper oxide is formed on the SiO ₂ substrate of the comparative example. The solar cell element structure for demonstrating the 1st Example of this invention. The spectral quantum efficiency characteristic of the solar cell element by the 1st example of the present invention. The manufacture flowchart for demonstrating the 2nd Example of this invention. The solar cell element structure for demonstrating the 3rd Example of this invention. The manufacturing flowchart for demonstrating the 3rd Example of this invention.

Hereinafter, specific structures, methods, procedures, and numerical values will be described in detail with reference to the drawings and data for the embodiments of the present invention.
First, the knowledge found by the inventors will be described. FIG. 1 shows the relationship between the Cu ₂ O film formation method and conditions and the Cu ₂ O crystallinity of the obtained film. Crystallinity is measured by X-ray diffraction (XRD). Fig. 1 (a) shows the XRD spectrum immediately after the Cu ₂ O film is formed on the SiO ₂ substrate by sputtering at room temperature (broken line) and after RTA (solid line), and Fig. 1 (b) shows the SiO ₂ substrate on the SiO ₂ substrate. Similarly, an XRD spectrum is shown when a Cu ₂ O film is formed after forming a Pt film by sputtering. In addition, in a very thin thin film of about 100 nm, a spectrum with sufficient intensity may not be obtained by ordinary XRD measurement. Therefore, if in-plane mode measurement can be performed, the orientation can be confirmed more precisely. FIG. 1 (c) shows an XRD spectrum after recrystallization by RTA after forming a Cu ₂ O film on a SiO ₂ substrate and FIG. 1 (d) on a Pt substrate. As the base substrate, a Si substrate was also used for comparison, but the result was very similar to that of the SiO ₂ substrate, and the description thereof will be omitted.

Details of the experimental conditions for obtaining the results of FIG. 1 are as follows.
Substrate: Si substrate on which 400 nm of SiO ₂ is formed by thermal oxidation (hereinafter referred to as “SiO ₂ substrate”).
A substrate in which Ta 20 nm and Pt 100 nm are sequentially laminated on the SiO ₂ substrate by sputtering.
(Hereafter referred to as “Pt substrate”).
Cu ₂ O film forming apparatus and forming conditions:
Equipment: rf magnetron sputtering equipment Applied power frequency: 13.56MHz
Target-board spacing: 100mm (board is rotating eccentrically)
Target size: 101.6mmφ
Substrate temperature: Room temperature (no control, substrate stage temperature measured 25-35 ° C)
Target: Cu ₂ O sintered ceramics, purity 2N (99%), metal impurities <0.1%
Ar flow rate: 25sccm
O ₂ flow rate: 0.4 sccm (O ₂ flow rate ratio = O ₂ / (O ₂ + Ar) = 1.6%)
Total gas pressure (Ar + O ₂ ): 0.5Pa
Discharge power: 3.82W / cm ²
Cathode (target) peak-to-peak voltage Vp-p: 450V
RTA conditions:
Atmosphere: Ar / O ₂ , 1 atm (O ₂ partial pressure: 1.0 Pa)
Temperature increase rate: 15 K / s
Processing temperature: 600 ℃
Processing time: 30s
Temperature drop rate: Not set (natural cooling in Ar 600 ℃ → 100 ℃, 18min)

In the sputtering method using a Cu ₂ O ceramic target, a Cu ₂ O single-phase polycrystalline thin film can be formed by precisely adjusting the small amount of O ₂ flow rate ratio in Ar plasma.
The broken line in FIG. 1A shows an XRD spectrum immediately after 100 nm is formed on the SiO ₂ substrate by sputtering at room temperature. Since the XRD spectrum shows only peaks derived from Cu ₂ O, it can be confirmed that the film immediately after the formation is a single crystal phase consisting of only the Cu ₂ O crystal phase, but the (111) plane and (200) A plurality of peaks of the surface are observed, and it can be seen that the plane orientations of the crystal grains are not aligned. When this Cu ₂ O film is subjected to RTA treatment, each peak intensity greatly increases and the half width (FWHM) becomes a steep spectrum narrow, so it can be seen that growth of the crystal grain size occurs, It can be seen that the crystal grains having respective plane orientations grow in a plurality of directions while maintaining the initial orientation.

On the other hand, FIG. 1B shows the results when a Cu ₂ O single phase film is formed to 100 nm on a Pt substrate. The largest diffraction peak is Pt (111), and it can be seen that the underlying Pt is very strongly oriented in the (111) plane. Originally, a metal with a face-centered cubic structure, when deposited on an amorphous surface, spontaneously arranges (111) plane orientation because each atom tries to be arranged in a six-way closest packing so that the surface energy is minimized. Tend to. The diffraction peak intensity of the Cu ₂ O film immediately after it is formed on this Pt (111) film at room temperature is very weak and a slight (111) plane orientation is observed. It can be seen that when this Cu ₂ O film is subjected to RTA treatment, the Cu ₂ O (111) plane peak becomes much stronger and the FWHM becomes very narrow. The peak of the Pt (111) plane spreads to the high angle side after RTA because the Pt polycrystal film surface is in the lateral direction as the crystal growth of Cu ₂ O has a lattice constant about 9% larger than that of Pt. This is because distortion occurs so that the distance between the (111) planes in the vertical direction is reduced.
In-plane measurement can confirm the crystal plane orientation perpendicular to the substrate surface, but shows the orientation of the Cu ₂ O film formed on the SiO ₂ substrate and recrystallized by RTA. Then, the three directions of (111), (200), and (220) are confirmed, and it can be confirmed that the directions of the crystal grains are not aligned. On the other hand, in FIG. 1 (d) showing the orientation of the Cu ₂ O film on the Pt film, peaks of (110) and (220) are confirmed, which are (111) oriented with respect to the surface. Since this spectrum shows a plane equivalent to the vertical plane component of the crystal, the Cu ₂ O film can be said to be completely (111) oriented with respect to the substrate surface.

2A and 2B are a cross-sectional TEM photograph of the sample after RTA in FIGS. 1A and 1B and a trace view thereof. It can be seen that the Cu ₂ O film formed on the SiO ₂ substrate-1 has crystal grains oriented in various directions like a random stonework (FIG. 2-10). On the other hand, in the Cu ₂ O film formed on the Pt substrate-3, crystal grains having almost the same height as the film thickness are ordered (that is, most crystal grains are exposed on both sides of the polycrystalline film). (Figure 2-4). Further, from the result of FIG. 1B, it can be said that the orientation planes are aligned to (111) in almost all crystal grains.

FIG. 3 shows the result of comparing the crystallinity of both by photoluminescence (PL). The excitation wavelength is 532 nm and the measurement temperature is 10K. From the Cu ₂ O film formed on the SiO ₂ substrate, almost no clear PL can be observed even at a low temperature of 10K, and it can be seen that various crystal defects remain at high density even after the RTA treatment. On the other hand, in the Cu ₂ O film formed on the Pt substrate, multiple modes of PL are observed, and in particular, the band edge emission (Xo) is clearly seen. By adopting a structure that aligns in one direction and eliminates the grain interface in the thickness direction, even a polycrystalline film formed at a low process temperature exhibits excellent properties that are close to a single crystal, resulting in the entire film. It has become clear that the characteristics of

When the hole mobility at room temperature of the Cu ₂ O film formed on the SiO ₂ substrate by the Van der Pauw method was confirmed, a value of 16 cm ² / Vs was obtained. Since the maximum value of mobility of the Cu ₂ O single crystal reported at present is about 100 cm ² / Vs, the mobility of the Cu ₂ O polycrystalline film formed on the SiO ₂ substrate is still low. However, from the PL comparison results, it is considered that the Cu ₂ O film formed on the Pt substrate has a value larger than at least the mobility on SiO ₂ and close to single crystal Cu ₂ O. Although Cu ₂ O film on Pt is the mobility of the film for the base is unable Hall effect measurement in the same way for the conductor unknown, because probably in the horizontal direction there are many grain boundaries, SiO ₂ upper It is considered to be an anisotropic mobility characteristic in which the mobility is greatly improved in the film thickness direction.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to this Example.

(Example 1)
FIG. 4 shows the structure of the solar cell element in this example. Hereinafter, the structure and the manufacturing method will be described while following the manufacturing procedure.
The substrate-1 is a SiO ₂ substrate formed by thermal oxidation on a Si wafer. On this thermally oxidized substrate, a 20 nm Ta layer-2 and a 100 nm Pt layer-3 are continuously laminated at room temperature by magnetron sputtering. The Ta layer-2 is not necessarily required, but is preferably inserted in order to improve the adhesion between the Pt layer-3 and the SiO ₂ substrate. The Pt layer-3 serving as the lower electrode is spontaneously (111) -oriented at this point and may be used as it is, but preferably about 600 ° C. (for example, 550 to 620 ° C., preferably 580 to 610 It has been confirmed that the surface smoothness of the Cu ₂ O layer to be formed later is improved when RTA is performed at a temperature of (° C.) and stress relaxation of the film generated during sputtering and slight crystal grain growth are performed. . If the RTA temperature at this time greatly exceeds 600 ° C., the surface smoothness is deteriorated.

Next, the Cu ₂ O layer that becomes the light absorption layer is formed at a low temperature of room temperature to 400 ° C. according to the required amount of about 100 to 1000 nm by magnetron sputtering using a Cu ₂ O sintered ceramic target (Example) Data is formed at room temperature). At this time, since the Cu ₂ O layer is formed at a relatively low temperature, it is a polycrystalline film having a relatively small grain size, but under the influence of the (111) crystal orientation plane of the underlying Pt layer-3, These crystal grains are in a columnar crystal state that already has orientation.
Next, this substrate is subjected to RTA treatment for 30 seconds to 5 minutes while precisely controlling the atmospheric gas so that the treatment temperature is 400 to 600 ° C. and the oxygen gas partial pressure is in the range of 0.1 to 10 Pa, and a Cu ₂ O layer Is recrystallized to form a Cu ₂ O layer-4 in which all the crystal grains are oriented in the (111) plane and the crystal thickness is almost one crystal grain. The RTA temperature, time, and oxygen gas partial pressure are adjusted according to the thickness of the deposited Cu ₂ O layer-4.
Note that all of the crystal grains of Cu ₂ O layer is oriented in (111) plane (i.e., that the crystal plane orientation of each crystal grain is selected only in one direction) is, Cu ₂ O In the XRD spectrum of the film, substantially only the (111) plane peak is observed, that is, the peak area can be confirmed by appearing with a size of 90% or more of the total peak area derived from Cu ₂ O. it can. In order to confirm the orientation more precisely, in-plane measurement mode is used to measure the XRD spectrum in the direction perpendicular to the surface, and the (110) plane and (220) which are substantially equivalent to the plane perpendicular to the (111) plane. ) Only the peak of the surface is observed, that is, the area of the peak appears at 90% or more of the total peak area derived from Cu ₂ O.

Next, a thin Cu ₂ O layer (10 nm) and a thin ZnO layer (10 nm) were continuously deposited in vacuum at room temperature by magnetron sputtering, and then heat-treated again at 400 ° C. for 30 s with RTA, and the p / n interface. Form layer-5.
Next, a ZnO buffer layer (10 nm) -6 is formed by magnetron sputtering.
Next, an AZO layer-7 to be an n-type layer is deposited by 1000 nm by a dc-magnetron sputtering method.
Finally, the contact electrode-9 of the comb-shaped upper electrode-8 and the Pt layer-3 serving as the lower electrode is simultaneously formed by vapor deposition using an Al source to complete the solar cell element.
FIG. 5 shows an example of the spectral quantum efficiency of the solar cell element in the case where the Cu ₂ O layer thickness is 0.2 μm formed by the above method. It was confirmed that a sufficient quantum efficiency can be obtained from the near ultraviolet region to the visible light region of 600 nm even with a light absorption layer thickness of 1/500 of the conventional example with a Cu ₂ O layer thickness of 0.2 μm.

Detailed conditions omitted in the above description are summarized below.
<Cu ₂ O layer-4 formation conditions and film properties>
Target: Cu ₂ O sintered body, purity 2N (99%)
Substrate temperature: Room temperature to 400 ° C (Example data is room temperature)
Discharge: rf discharge mode
Ar flow rate: 25sccm
O ₂ flow rate: 0.4ccm
O ₂ addition rate: 1.6%
Total gas pressure: 0.5Pa
Discharge power: 3.82W / cm ²
Cathode (target) peak-to-peak voltage Vp-p: 450V
Resistivity: 2.7 × 10 ⁵ Ωcm
Film thickness: 100-1000nm
<RTA>
Atmosphere: Ar / O ₂ 1atm (O ₂ partial pressure: 1Pa)
Temperature increase rate: 15K / s
Processing temperature: 400-600 ℃
Processing time: 30-300s
Temperature drop rate: Not set (600 ℃ → 100 ℃, 18min)

<Formation conditions and film characteristics of ZnO buffer layer-6>
Target: ZnO, purity 4N (99.99%)
Target size: 80mmφ
Substrate temperature: room temperature Discharge: rf discharge mode
Ar flow rate: 23sccm
O ₂ flow rate: 2sccm
O ₂ addition rate: 8%
Total gas pressure: 0.5Pa
Discharge power: 7.96W / cm ²
Cathode (target) peak-to-peak voltage Vp-p: 990V
Resistivity: 3 × 10 ⁶ Ωcm
Film thickness: 10nm

<Formation conditions and film characteristics of AZO layer-7>
Target: ZnO: Al ₂ O ₃ = 98: 2, purity 4N (99.99%)
Target size: 101.6mmφ
Substrate temperature: room temperature Discharge: DC discharge mode
Ar flow rate: 25sccm
O ₂ flow rate: 0sccm
O ₂ addition rate: 0%
Total gas pressure: 0.5Pa
Discharge power: 2.55W / cm ²
Cathode (target) voltage: 440V
Resistivity: 2.3 × 10- ³ Ωcm

(Example 2)
Although the solar cell having sufficient sensitivity shown in FIG. 5 can be formed by the method described in Example 1, in FIG. 5, the sensitivity in the light wavelength band of 500 nm to 600 nm is slightly low. This is because the light absorption coefficient of Cu ₂ O in this region is very small. If the Cu ₂ O layer is made thicker, the sensitivity in this region is further improved. For this reason, a means for further increasing the thickness of the Cu ₂ O layer will be described based on Example 2.
When a Cu ₂ O film having a thickness of 1 μm or more is deposited by the method shown in Example 1, the Cu ₂ O polycrystalline film may not be strongly (111) -oriented even if the grain growth process is performed by RTA. It is effective to increase the film thickness while maintaining the orientation by repeating the Cu ₂ O film forming process a plurality of times. FIG. 6 shows a flowchart of the procedure. Conditions for each process in the flowchart are the same as those described in the first embodiment unless otherwise specified.

First, a substrate on which a Pt film as a base is formed is prepared. Next, a Cu ₂ O film is formed at a low temperature of room temperature to 400 ° C. using a sputtering method. Next, recrystallization is performed at a temperature of 400 ° C. to 600 ° C. by RTA treatment. Next, reverse sputtering is performed by argon gas discharge in a sputtering apparatus, and the formed Cu ₂ O surface is removed by a thickness of about 5 nm, and then a Cu ₂ O film is stacked and formed by sputtering. This sputter deposition, RTA, and reverse sputtering processes are repeated until a desired film thickness is obtained. When the desired film thickness is reached, the structure of the solar cell element is formed by performing Cu ₂ O / ZnO interface formation, interface RTA treatment, ZnO buffer layer formation, AZO layer formation, and electrode deposition in the same procedure as in Example 1. Complete. By stacking and depositing the Cu ₂ O layer by such a method, it is possible to obtain a light absorption layer in which the crystal grain interface is reduced in the film thickness direction without disturbing the (111) plane orientation. In order to obtain an ideal Cu ₂ O layer as much as possible, it is preferable to set the deposited film thickness to be thin within a range of 100 to 200 nm, but the number of process steps increases. However, in this case, the sputter deposition time can be shortened because the sputter deposition temperature can be room temperature. On the other hand, when increasing the thickness of a single deposited film, it is effective to set the deposition temperature higher in the range up to 400 ° C., but the waiting time for the sputtering process becomes longer. Because of these trade-offs, it is preferable to determine the optimum process by comprehensively considering the required solar cell specifications and manufacturing process environment.

Detailed conditions omitted in the above description are summarized below.
<Reverse sputtering conditions>
Discharge: rf discharge mode
Ar flow rate: 25sccm
Ar gas pressure: 0.5Pa
Discharge power: 0.13W / cm ²
Board voltage: -380V

(Example 3)
In the solar cell using the Cu ₂ O crystal structure according to the present invention, ideal electrical characteristics closer to a single crystal can be obtained as the Cu ₂ O layer thickness is thinner. For this reason, when a light confinement structure is added in a region thinner than the thickness required for the light absorption coefficient as a bulk material, in addition to the increase in light absorption due to the light confinement effect, various crystal defects are caused Since the charge loss is greatly reduced, the solar energy conversion efficiency is significantly improved. In order to utilize such an action, a structure of a surface plasmon resonance type solar cell element using a metal nanodot antenna and a manufacturing method thereof will be described.

FIG. 7 shows a solar cell element structure in which nanodots are added by sputtering of Ag directly on a thin ZnO buffer layer-6 in order to form surface localized plasmons at a shallow position of the Cu ₂ O layer. The light wavelength that causes plasmon enhancement depends on the dots of the metal nanodot antenna and the gap between the dots. In order to selectively enhance the electric field strength in the 500 to 600 nm wavelength region where the light absorption coefficient of the Cu ₂ O film greatly decreases, it is appropriate that the Ag dot size is about 20 nm and the gap between dots is about 1 to 5 nm. It is. FIG. 8 shows a flowchart of the procedure. Conditions for each process in the flowchart are the same as those described in the first embodiment unless otherwise specified.

First, a substrate-1 on which a Pt film-3 as a base is formed is prepared. Next, a Cu ₂ O film-4 is formed at room temperature using a sputtering method. Next, Cu ₂ O / ZnO interface formation, interface RTA treatment, and ZnO buffer layer-6 formation are performed in the same procedure as in Example 1. Next, Ag is deposited to about 15 to 30 nm by vapor deposition while heating the substrate-1 on which these layers are formed to 200 to 400 ° C. At this time, since the underlying Cu ₂ O layer-4 is strongly oriented in the (111) plane, the interface layer-5 and the ZnO buffer layer-6 are also influenced by it and have a certain degree of plane orientation, The underlying ZnO buffer layer-6 is (0001) -plane oriented. Since the Ag fine particles adhering to the surface of the ZnO buffer layer-6 during the sputter deposition are aggregated and grown in an (111) plane orientation, the nanodot structure-11 is formed in a self-organized manner. Next, AZO layer-7 is formed and electrode deposition is performed to complete the structure of the solar cell element. The nanodot antenna structure can be replaced with a metal such as Au or Cu.
In addition, in the solar cell element using the Cu ₂ O film polycrystalline structure according to the present invention, in addition to the surface plasmon resonance, an optical confinement structure such as an optical interference effect or light scattering is used. However, it is likely that good results will be obtained.

Having described the embodiments of the present invention in detail above, since one of the features portion of the present invention is a crystal structure itself of the Cu ₂ O layer -4, the deposition conditions of the Cu ₂ O layer -4, Example For example, a metal Cu target may be used as a sputtering target, and if a Cu ₂ O film is deposited, copper oxide powder is used as a thin film forming method. Any method can be applied, such as a vacuum deposition method using as a source, a PLD method for evaporating a target with a pulse laser, or an MOCVD method using an organic metal gas material. In addition, as the solar cell element structure, any structure and material other than the crystal structure of the Cu ₂ O film-4 serving as a light absorption layer can be used as long as it is a combination that forms a p / n heterojunction with Cu ₂ O. Any material can be applied.

  As described above, according to the present invention, it is possible to significantly reduce the temperature of the conventional manufacturing process, so that it can be used in a wide range of fields. In particular, considering the equipment to be used and the manufacturing method, it is highly compatible with the manufacturing process of various semiconductor devices. There is a possibility that it can be used for a device having a concept that has not been conventionally used, such as a memory device, a logic device, or a sensor device.

1 SiO ₂ substrate 2 Ta layer 3 Pt film 4 (111) oriented Cu ₂ O polycrystalline film consisting of a single crystal grain in the film thickness direction 5 Cu ₂ O / ZnO interface layer 6 ZnO buffer layer 7 AZO layer 8 Upper comb electrode 9 Lower contact electrode 10 Cu ₂ O polycrystalline film 11 having irregular crystal orientation plane Ag nanodot antenna

Claims (7)

A semiconductor device comprising a Cu ₂ O film as a p-type semiconductor layer, wherein the Cu ₂ O film has a thickness of 100 to 1000 nm, wherein the crystal plane orientation direction of each crystal grain is selected in only one direction And 80% or more of the crystal grains constituting the polycrystalline film are exposed on both sides of the polycrystalline film. An oxide solar cell element comprising a Cu ₂ O film as a p-type semiconductor layer, wherein the Cu ₂ O film has a thickness selected so that the crystal plane orientation direction of each crystal grain is only in one direction. An oxide solar cell element characterized in that it is a polycrystalline film of 100 to 1000 nm, and 80% or more of the crystal grains constituting the polycrystalline film are exposed on both sides of the polycrystalline film. On the substrate, a metal film having a face-centered cubic lattice atomic arrangement structure having a work function value equal to or higher than that of Cu ₂ O as a lower electrode, the Cu ₂ O film, a ZnO layer as a buffer layer, and The oxide solar cell element according to claim 2, comprising AZO layers as n-type semiconductor layers in this order and having a heterojunction diode structure.   The oxide solar cell element according to claim 3, further comprising a metal nanodot antenna structure for generating surface plasmon resonance immediately above the ZnO buffer layer.   5. The oxide solar cell element according to claim 3, wherein the metal film is selected from a Pt film, an Au film, a Ni film, a Pd film, and an Ir film. A metal film forming step of forming a metal film having a face-centered cubic lattice atomic arrangement structure having a work function value equal to or greater than that of Cu ₂ O on a substrate; a p-type semiconductor directly on the metal film; Cu ₂ O film deposition step of depositing a Cu ₂ O layer as the layer at a temperature from room temperature to 400 ° C., and, by performing the heat treatment of oxygen partial adjust the pressure in the range of 0.1~10Pa while 400 ° C. to 600 ° C. Cu ₂ O film manufacturing method of a semiconductor element or an oxide solar cell device according to any one of claims 1 to 5, a recrystallization heat treatment step of performing recrystallization comprises at least. The Cu ₂ O deposited film thickness of the single Cu ₂ O film deposition step was 200nm with maximum semiconductor device according to a Cu ₂ O layer deposition step and subsequent recrystallization heat treatment process in claim 6 are repeated a plurality of times or A method for manufacturing an oxide solar cell element.

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